Regarding the soft start, it's fine with one power relay, if you can find one that's big enough (they do exist, but be aware of the coil current for the big relays!)
Also, you mey find relays with two current ratings like 8(1)A. this means that it is designed to switch 1A resistive load (wherever you'd find that!?), but only 1A when the load cintains reactive components (like your transformer). This is because reactive loads generate high voltage spikes when switched off, and cause higher currents when switched on. Both things reguire more from the relay, in terms of materials and dimensioning. The high inrush current is not relevant here, but the voltage peaks (when swithing off) are still present. Thus, I recomment you use a properly rated relay, despite the inrush circuit. Basically, it all comes down to life time interms of on/off cycles of the relay. In extreme cases, a relay (or other switch) which is not designed properly for inductive loads, can catch on fire after lots of switching cycles due to the arcing, chich friefly cooks the inside of the relay enclosure. This causes the material to "burn" on the surface, causing carbon tracks. This is conductive, and after a while, this starts to act as an uncontrolled resistive path for current. Resistors generate heat, which causes more carbon to form... you get the picture?
SOOoooo... Choose wisely
Typically me, I've gone overkill and chosen industrial relays rated 250V, 30 (20) Amps. They draw 12V, 250mA for the coil. They give a cool audible >CLICK<, too.
Jennice
Also, you mey find relays with two current ratings like 8(1)A. this means that it is designed to switch 1A resistive load (wherever you'd find that!?), but only 1A when the load cintains reactive components (like your transformer). This is because reactive loads generate high voltage spikes when switched off, and cause higher currents when switched on. Both things reguire more from the relay, in terms of materials and dimensioning. The high inrush current is not relevant here, but the voltage peaks (when swithing off) are still present. Thus, I recomment you use a properly rated relay, despite the inrush circuit. Basically, it all comes down to life time interms of on/off cycles of the relay. In extreme cases, a relay (or other switch) which is not designed properly for inductive loads, can catch on fire after lots of switching cycles due to the arcing, chich friefly cooks the inside of the relay enclosure. This causes the material to "burn" on the surface, causing carbon tracks. This is conductive, and after a while, this starts to act as an uncontrolled resistive path for current. Resistors generate heat, which causes more carbon to form... you get the picture?
SOOoooo... Choose wisely
Typically me, I've gone overkill and chosen industrial relays rated 250V, 30 (20) Amps. They draw 12V, 250mA for the coil. They give a cool audible >CLICK<, too.
Jennice
Here is a starting point...
Here is starting point for you - Duncan's simulator Here is a simple freeware simulation software for designing unregulated power supplies like the ones you are needing here. It has more details than you really need, and like alot of things, the accuracy of the details is totally dependent upon the skill of the operator.
BUT its a great learning tool.
Here is starting point for you - Duncan's simulator Here is a simple freeware simulation software for designing unregulated power supplies like the ones you are needing here. It has more details than you really need, and like alot of things, the accuracy of the details is totally dependent upon the skill of the operator.
BUT its a great learning tool.
Transformer ratings, written on the transformer itself, are normally before rectification. The Transformer manufacturer doesn't know what you're going to do with the output, so he rates his product as stand-alone.
A secondary rating of 40-0-40V means it's 40V-0-40V ac with a center tab. (it will have three secondary wires sticking out from the X-former.)
This is often stated as the rated voltage under nominal load. since a transformer has losses, it has a non-zero output impedance. Thus, the output voltage will be load-dependent.
A full-bridge rectified voltage will be roughly 1.4*Vac (1.4 being roughly the square root of 2), in this case 1.4*40 = 56Vdc, loaded. Idle will be often be higher, depending on transformer type and size. Bigger X-formers have lower output impedence (obviously, you may say). From there, you should subtract 2 diode voltage drops of 0.7V each= 1.4V which leaves 54.6Vdc. Then again, you will often measure a higher voltage, as you're not measuring at rated transformer load, which you should never reach when using it with rectifiers, anyway.
I would use higher ratings than 63V for the following capacitors (80V is more suitable), as idle voltages will be higher than 54V, and you will encounter mains fluctuations, also.
A real lifer example: The transformers for my current project are rated 2*36V/7A secondary (two seperate secondaries). My goal is about 50 to 51V , and they have 4% load regulation according tot the manufacturer (the drop from idle voltage to volage under rated load).
36Vac * 1,4 gives 50.4Vdc. This is at rated load, which is what I asked for. I know I don't have the 1.4V considered, but I'm not going to load them fully either. Load regulation means that my idle voltage should be 50.4 / (1-0,04) = 50.4 / 0.94 = 53.5Vdc idle. I measured about 54.1V idle, so I think I got what I requested.
I am optimistic, and will be using a stack of 63V capacitors I have to spare for the project. If my stock was empty I would consider using 80V types, too.
Hope this helps.
Jennice
A secondary rating of 40-0-40V means it's 40V-0-40V ac with a center tab. (it will have three secondary wires sticking out from the X-former.)
This is often stated as the rated voltage under nominal load. since a transformer has losses, it has a non-zero output impedance. Thus, the output voltage will be load-dependent.
A full-bridge rectified voltage will be roughly 1.4*Vac (1.4 being roughly the square root of 2), in this case 1.4*40 = 56Vdc, loaded. Idle will be often be higher, depending on transformer type and size. Bigger X-formers have lower output impedence (obviously, you may say). From there, you should subtract 2 diode voltage drops of 0.7V each= 1.4V which leaves 54.6Vdc. Then again, you will often measure a higher voltage, as you're not measuring at rated transformer load, which you should never reach when using it with rectifiers, anyway.
I would use higher ratings than 63V for the following capacitors (80V is more suitable), as idle voltages will be higher than 54V, and you will encounter mains fluctuations, also.
A real lifer example: The transformers for my current project are rated 2*36V/7A secondary (two seperate secondaries). My goal is about 50 to 51V , and they have 4% load regulation according tot the manufacturer (the drop from idle voltage to volage under rated load).
36Vac * 1,4 gives 50.4Vdc. This is at rated load, which is what I asked for. I know I don't have the 1.4V considered, but I'm not going to load them fully either. Load regulation means that my idle voltage should be 50.4 / (1-0,04) = 50.4 / 0.94 = 53.5Vdc idle. I measured about 54.1V idle, so I think I got what I requested.
I am optimistic, and will be using a stack of 63V capacitors I have to spare for the project. If my stock was empty I would consider using 80V types, too.
Hope this helps.
Jennice
OK, that makes sense. On my Haflers I get a reading of +/-45V without the filter caps hooked up and +/-63V with.
So then, if an amp calls for +/-70V rails I should shoot for a transformer that is rated at 70V / 1.414 = 49-0-49? Does that sound right?
I have a couple of more questions. What is the advantage of using say six, 4700uf,75V filter caps, rather than two, 15000,75V caps?
Also, I emailed Rod Elliot about using my two Hafler trannies to power the three P101 boards and this was his response:
Terry,
Have a look at http://sound.westhost.com/power-supplies.htm - Figure 4
shows a full wave rectifier. Use one of these from each of your
transformers, with the -ve of one connected to ground, and the +ve of
the other grounded. That gives you a +/- supply with zero interaction
between transformers. There is no loss of fidelity - the two
transformers act as one.
Alternatively, connect the two transformers conventionally, using 2
bridge rectifiers, and common the +ve and -ve outputs of the rectifiers
(i.e. +ve of one to +ve of the other, and same for the -ve). There are
many ways this can be done, and there is more info in the construction
section.
You will want to increase the capacitance, and the supply scheme shown
in the construction guide can still be used.
Have you guys got a preference to which way you would do this?
Thanks, Terry
So then, if an amp calls for +/-70V rails I should shoot for a transformer that is rated at 70V / 1.414 = 49-0-49? Does that sound right?
I have a couple of more questions. What is the advantage of using say six, 4700uf,75V filter caps, rather than two, 15000,75V caps?
Also, I emailed Rod Elliot about using my two Hafler trannies to power the three P101 boards and this was his response:
Terry,
Have a look at http://sound.westhost.com/power-supplies.htm - Figure 4
shows a full wave rectifier. Use one of these from each of your
transformers, with the -ve of one connected to ground, and the +ve of
the other grounded. That gives you a +/- supply with zero interaction
between transformers. There is no loss of fidelity - the two
transformers act as one.
Alternatively, connect the two transformers conventionally, using 2
bridge rectifiers, and common the +ve and -ve outputs of the rectifiers
(i.e. +ve of one to +ve of the other, and same for the -ve). There are
many ways this can be done, and there is more info in the construction
section.
You will want to increase the capacitance, and the supply scheme shown
in the construction guide can still be used.
Have you guys got a preference to which way you would do this?
Thanks, Terry
Check out this site for more info details, about power supplies.
http://zero-distortion.com/start.htm
Prosit
http://zero-distortion.com/start.htm
Prosit
still4given said:
Except for load regulation, yes. The problem is that idle voltage is higher than "rated voltage". If ESP's limit is 70V due to some component ratings, you risk destroying it when switching on (before the transformers are loaded with the speaker via the amp). I would ignore the extra watts (you won't hear them much anyway), and live happily (and cheaper and safer) with your existing transformers.
Lower (better) ESR and ESL. The output impedance will be lower, provided that the capacitors are the same basic build concept.
Look at the figure on the bottom of page 6 of my notes (PDF file). You'll parallel the ESR and ESL's to get a lower overall figure, when paralleling 3 caps. You can try to figure out the true numbers from a capacitor data sheet.
Yes, I'd certainly use option one. You'll get un-equal loading and a lot of transients from the diodes when going for option 2.
Caps are annoyingly expensive, but I agree with Rod, that you will want more than 15000uF for each supply rail. For your kind of amp I would go more like 3 times that for each rail, or even more.
Personally I don't believe you can ever get too many capacitors in an amp.
The more capacity, the lower the apparent output impedance of your PSU (Power Supply Unit). In the end, the power will have to come from the transformer, so caps are no excuse for a small transformer, but a big transformer with small caps will just cause lots of ripple, and medicore output impedance.
I'm using 50.000 uF for each supply rail of the 2x150W amp I'm currently building.
The power supply will (when done right) always be an expensive part of your power amps. You might as well get used to it.
When I design an amp, about half the budget goes to the supply.
Jennice
still4given said:
No, there shouldn't be. Actually I sure hope not, 'cause I'm planning on using such. Never heard of a problem with it, anyway.
I'm using mine up-side-down in cap.holders for good mechanical stability, and then hardwiring them. If you use them as intended on a PCB, consider hotmelt or glue or silicone as strain-releaf (how's that spelled correctly? Hmm...
) The aim is to avoid the mechanical stress being on the terminals alone.I don't know... haven't tried them, nor seen a data sheet. Got a link for us (and a reference to the type ypu have in mind)?
Actually, I was thinking more about 10,000uF, 80V or 15,000uF, 80V. If I use 3 per rail, do I have to do anything special to the rest of the circuit in order to handle the greater values?
I am still planning on building a soft-start circuit, although I'm not real clear on where in the circuit to employ it. Does it go before the transformer?
I would like to get the Filter caps ordered if you think these values would work and if the Cornell Dubilier brand is suitable.
Blessings, Terry
I am still planning on building a soft-start circuit, although I'm not real clear on where in the circuit to employ it. Does it go before the transformer?
I would like to get the Filter caps ordered if you think these values would work and if the Cornell Dubilier brand is suitable.
Blessings, Terry
Hi Terry,
For comparison, I have taken datas for the 12.000 uF/80V version, which is both manufactured by C.D. (the one you suggest) and by Nippon Chemi-Con (the ones I use for my current project).
C.D.'s data is:
uF Product number ESR at Ripple(A) Size
120 Hz 120Hz Diam.x height
12000 382LX123M100N082 0.028 0.021 8.65 10.00 40x80
12000 380LX123M100A102 0.028 0.021 8.57 9.86 35x105
These two variants are virtually identical.
The Nippon's are:
12.000 uF, ESR at 120 Hz is 0.021 ohm, Ripple max 5.72A, and size is 35x80mm
The ESR in yours creates a little higher losses, but they are also bigger and can dissapate the heat created, thereby allowing a higher ripple current.
My personal guess is that you'll be fine with 45.000 uF or more per rail, if you want to drive 2 channels from the same supply.
One can never get enough capacity (I know... I'm repeating myself), but I think you're on the right track.
A word of warning: Even on the secondary side, the voltage is high enough to cause injury, especially if you (prove to?) have a weak heart (easily affected by electric shocks). Be careful, and don't work on it if you're feeling tired. Dis-charge the capacitors before working with them. Do NOT - NEVER !!! - discharge them with a piece of wire. Especially when paralleled. A normal wire (or tin solder, god forbid!!!!) will weld or evaporate. It's not a joke. Before tsaking the time to do the math, I learned it the hard way. Good thing I wear glasses every day...!
Always use something with reasonable resistance, such as a power resistor 47-100 ohm), or a light bulb. I know it sounds odd, but it works perfectly ok to use a light bulb (in appropriate socket!) to discharge them. As you'll end up with more than 110V rail-to-rail, take one side at a time, or your bulb won't last long.
The soft start relay goes on the primary side (on the side that goes to the wall outlet). Try reading ESP's page on this project again very carefully.
Jennice
For comparison, I have taken datas for the 12.000 uF/80V version, which is both manufactured by C.D. (the one you suggest) and by Nippon Chemi-Con (the ones I use for my current project).
C.D.'s data is:
uF Product number ESR at Ripple(A) Size
120 Hz 120Hz Diam.x height
12000 382LX123M100N082 0.028 0.021 8.65 10.00 40x80
12000 380LX123M100A102 0.028 0.021 8.57 9.86 35x105
These two variants are virtually identical.
The Nippon's are:
12.000 uF, ESR at 120 Hz is 0.021 ohm, Ripple max 5.72A, and size is 35x80mm
The ESR in yours creates a little higher losses, but they are also bigger and can dissapate the heat created, thereby allowing a higher ripple current.
My personal guess is that you'll be fine with 45.000 uF or more per rail, if you want to drive 2 channels from the same supply.
One can never get enough capacity (I know... I'm repeating myself), but I think you're on the right track.
A word of warning: Even on the secondary side, the voltage is high enough to cause injury, especially if you (prove to?) have a weak heart (easily affected by electric shocks). Be careful, and don't work on it if you're feeling tired. Dis-charge the capacitors before working with them. Do NOT - NEVER !!! - discharge them with a piece of wire. Especially when paralleled. A normal wire (or tin solder, god forbid!!!!) will weld or evaporate. It's not a joke. Before tsaking the time to do the math, I learned it the hard way. Good thing I wear glasses every day...! Always use something with reasonable resistance, such as a power resistor 47-100 ohm), or a light bulb. I know it sounds odd, but it works perfectly ok to use a light bulb (in appropriate socket!) to discharge them. As you'll end up with more than 110V rail-to-rail, take one side at a time, or your bulb won't last long.
The soft start relay goes on the primary side (on the side that goes to the wall outlet). Try reading ESP's page on this project again very carefully.
Jennice
OK, I bought these. I figure it won't hurt to have some extra caps around.
Actually, I'm planning on driving 3 channels form this PSU. That's why I am using two trannies. I could always add a couple more caps if you think it's needed.
I hate getting shocked. I will definately treat things with great care.
Oh, one more question. The ESP kit calls for a 2.7ohm/1W resister. I can't seem to find one anywhere.
Any ideas where I can buy three of these?
Also, I need three 150ohm/5W resistors. Same thing, I can't fine them.
Blessings, Terry
Actually, I'm planning on driving 3 channels form this PSU. That's why I am using two trannies. I could always add a couple more caps if you think it's needed.
I hate getting shocked. I will definately treat things with great care.
Oh, one more question. The ESP kit calls for a 2.7ohm/1W resister. I can't seem to find one anywhere.
Any ideas where I can buy three of these?
Also, I need three 150ohm/5W resistors. Same thing, I can't fine them.
Blessings, Terry
For buying components, try these. Their main target is the industry, and they have some handling fee, but they have a wide selection of components, and (although I only know for Denmark, where I live) it's possible to buy as a private person, also.
For driving 3 channels, I would use at least 5 caps per rail. If possible, you could consider to leave space for more caps if more are needed.
Well, you know what my thought about capacity is, but then again... there is a planet earth, to which I sometimes tend to loose connection.
For driving 3 channels, I would use at least 5 caps per rail. If possible, you could consider to leave space for more caps if more are needed.
Well, you know what my thought about capacity is, but then again... there is a planet earth, to which I sometimes tend to loose connection.
try www.digikey.com - they have a $25 minimum order. Also www.mouser.com. No minimum order and they have both parts you are looking for. You can probably get most of the rest of the parts you need at either place.
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